Apparatus for controlling a screen pointer that distinguishes between ambient light and light from its light source

ABSTRACT

An apparatus for controlling the position of a screen pointer for an electronic device having a display screen, includes a light source for illuminating an imaging surface with a plurality of light pulses, thereby generating reflected light pulses. A detection circuit is configured to sense light, distinguish between the reflected pulses and ambient light, and generate a low signal indication if the magnitude of the reflected pulses falls below a threshold value. An optical motion sensor generates digital images based on the reflected pulses. The motion sensor is configured to generate movement data based on the digital images. The movement data is indicative of relative motion between the imaging surface and the apparatus.

FIELD OF THE INVENTION

This invention relates generally to devices for controlling a pointer(cursor) on a display screen, and relates more particularly to anapparatus for controlling a screen pointer that distinguishes betweenambient light and light from its light source.

BACKGROUND OF THE INVENTION

The use of a hand operated pointing device for use with a computer andits display has become almost universal. One form of the various typesof pointing devices is the conventional (mechanical) mouse, used inconjunction with a cooperating mouse pad. Mechanical mice typicallyinclude a rubber-surfaced steel ball that rolls over the mouse pad asthe mouse is moved. Interior to the mouse are rollers, or wheels, thatcontact the ball at its equator and convert its rotation into electricalsignals representing orthogonal components of mouse motion. Theseelectrical signals are coupled to a computer, where software responds tothe signals to change by a ΔX and a ΔY the displayed position of apointer in accordance with movement of the mouse.

In addition to mechanical types of pointing devices, such as aconventional mechanical mouse, optical pointing devices have also beendeveloped. In one form of an optical pointing device, rather than usinga moving mechanical element like a ball, relative movement between animaging surface, such as a finger or a desktop, and photo detectorswithin the optical pointing device, is optically sensed and convertedinto movement information. Battery operated optical mice are currentlyavailable based on Agilent's ADNS-2020 and ADNS-2030 optical imagesensors. Other optical mice are available based on Agilent's ADNS-2001and ADNS-2051, as well as other optical image sensors.

In a typical optical mouse, a light emitting diode (LED) illuminates thesurface under the mouse. Under normal circumstances, the mouse bodyblocks ambient light from reaching the area of the navigation surfacevisible to the image sensor. However, when the mouse is lifted, ambientlight can provide strong amplitude (but out of focus) images to theimage sensor. It is desirable for the optical mouse sensor to report nomotion in such situations, as the user is either finished with mouseusage (e.g., the mouse is set aside) or is attempting to reposition thescreen pointer due to limited space on the navigation surface.

At present, optical mice use out-of-focus indications, low signalamplitude indications, or zero displacement answers fromcross-correlation, in order to detect a mouse lifted condition and keepthe screen pointer steady. For the out-of-focus technique, the picturesfrom the image array are typically passed through a high pass filter,and the output of the high pass filter provides an indication of whetherthe images are in focus or not. If the images are not in focus, it islikely that the surface under the mouse is not at the correct, normaldistance, and the mouse may have been lifted by the user. For the lowsignal amplitude technique, the total amount of signal output by theimage sensor, which could be comprised of both light bouncing off thesurface from the LED and ambient light, is measured. When the amplitudeof the signal out of the image sensor is low, an indication to stopmoving the screen pointer is generated. If a sufficient amount ofambient light strikes the image sensor when the mouse is lifted, a lowsignal amplitude signal will not be generated, and the screen pointermay continue moving. For the third technique (zero displacement answersfrom cross-correlation), images are captured and correlated in thenormal manner to determine how much motion has occurred. When the mouseis lifted, the captured images are typically blurry and appear to beessentially the same to the mouse, so the mouse typically, but notalways, reports zero motion in this situation, causing the screenpointer to stop moving.

These prior methods for detecting a mouse lifted condition are notalways reliable. In some cases, the screen pointer moves in anunpredictable path, or jitters in place, when it should remain still,which results in an annoyance to the user and an undesirable consumptionof power. If the mouse lifted condition is not detected, the mouse mayremain in a full power mode, rather than switching to a sleep mode. Fora battery-operated mouse, if the mouse is left upside down or is leftunused at the end of a desk for a long period of time, a large amount ofbattery power can be consumed by not detecting this condition andfreezing the screen pointer.

In addition, if there is a large amount of ambient light on the areaunder the mouse that is being imaged, this ambient light can interferewith navigation accuracy during normal use of the mouse.

SUMMARY OF THE INVENTION

One form of the present invention provides an apparatus for controllingthe position of a screen pointer for an electronic device having adisplay screen. The apparatus includes a light source for illuminatingan imaging surface with a plurality of light pulses, thereby generatingreflected light pulses. A detection circuit is configured to senselight, distinguish between the reflected pulses and ambient light, andgenerate a low signal indication if the magnitude of the reflectedpulses falls below a threshold value. An optical motion sensor generatesdigital images based on the reflected pulses. The motion sensor isconfigured to generate movement data based on the digital images. Themovement data is indicative of relative motion between the imagingsurface and the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of an optical mouse according to one embodiment ofthe present invention.

FIG. 2 is a block diagram illustrating major components of the opticalmouse shown in FIG. 1 according to one embodiment of the presentinvention.

FIG. 3A is an electrical schematic/block diagram illustrating lightsensing circuitry of the optical mouse shown in FIG. 1 with twocapacitors per photo detector according to one embodiment of the presentinvention.

FIG. 3B is a timing diagram illustrating the timing of control signalsfor the light sensing circuitry shown in FIG. 3A.

FIG. 4A is an electrical schematic/block diagram illustrating lightsensing circuitry of the optical mouse shown in FIG. 1 with onecapacitor per photo detector according to another embodiment of thepresent invention.

FIG. 4B is a timing diagram illustrating the timing of control signalsfor the light sensing circuitry shown in FIG. 4A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings, which form a parthereof, and in which is shown by way of illustration specificembodiments in which the invention may be practiced. It is to beunderstood that other embodiments may be utilized and structural orlogical changes may be made without departing from the scope of thepresent invention. The following detailed description, therefore, is notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims.

FIG. 1 is a top view of an optical mouse 10 according to one embodimentof the present invention. Mouse 10 includes plastic case 12, left mousebutton (LB) 14A, right mouse button (RB) 14B, and optical motion sensorchip 16. Sensor chip 16 is covered by plastic case 12, and is thereforeshown with dashed lines in FIG. 1.

FIG. 2 is a block diagram illustrating major components of optical mouse10 according to one embodiment of the present invention. Optical mouse10 includes light source 2, lenses 4 and 8, and optical motion sensor16. Optical motion sensor 16 includes photo detector array 148,electronic shutter 150, a plurality of sense capacitors 154A-154C(collectively referred to as sense capacitors 154), multiplexer 156,amplifier 157, analog to digital (A/D) converter 158, correlator 160,photo detector 162, amplifier 164, multiplier 166, low pass filter (LPF)168, comparator (COMP) 172, oscillator (OSC) 176, multiplier 178, lightcontroller 180, shutter controller 184, and system controller 186.

In one embodiment, the operation of optical motion sensor 16 isprimarily controlled by system controller 186, which is coupled to andcontrols multiplexer 156, A/D converter 158, correlator 160, shuttercontroller 184, and light controller 180. In operation, according to oneembodiment, light source 2 emits light that is directed by lens 4 ontosurface 6, which is a desktop or other suitable imaging surface, andreflected images are generated. In one embodiment, light source 2includes one or more light emitting diodes (LED's). Reflected light fromsurface 6 is directed by lens 8 onto photo detector array 148 and photodetector 162. Photo detector 162 and photo detectors in photo detectorarray 148 each provide a signal that varies in magnitude based upon theintensity of light incident on the photo detector. In one embodiment,photo detector 162 and the photo detectors in photo detector array 148are photo diodes.

Electronic shutter 150 is controlled by a shutter signal 182 fromshutter controller 184. When electronic shutter 150 is “open,” chargeaccumulates on sense capacitors 154, creating voltages that are relatedto the intensity of light incident on the photo detectors in array 148.When electronic shutter 150 is “closed,” no further charge accumulatesor is lost from sense capacitors 154. Multiplexer 156 connects eachsense capacitor 154 in turn to amplifier 157 and A/D converter 158, toamplify and convert the voltage from each sense capacitor 154 to adigital value. Sense capacitors 154 are then discharged throughelectronic shutter 150, so that the charging process can be repeated.

In one embodiment, light source 2 is controlled by shutter signal 182from shutter controller 184. When shutter signal 182 goes high, the highsignal causes light controller 180 to output a signal for turning onlight source 2. The high shutter signal 182 also causes electronicshutter 150 to open, thereby allowing charge to accumulate on sensecapacitors 154. When shutter signal 182 goes low, the low signal causeselectronic shutter 150 to close, and causes light controller 180 tooutput a low signal to turn off light source 2. In one form of theinvention, the signals output by light controller 180 are modulated byoscillator 176 and multiplier 178, thereby causing the light emitted bylight source 2 to be modulated in the same manner. The modulation oflight emitted by light source 2 is described in further detail below.

Based on the level of voltage from each sense capacitor 154, A/Dconverter 158 generates a digital value of a suitable resolution (e.g.,one to eight bits) indicative of the level of voltage. The digitalvalues represent a digital image or digital representation of theportion of the desktop or other imaging surface under optical mouse 10.The digital values are stored as frames within correlator 160.

In addition to providing digital images to correlator 160, A/D converter158 also outputs digital image data to shutter controller 184 in oneform of the invention. Shutter controller 184 helps to ensure thatsuccessive images have a similar exposure, and helps to prevent thedigital values from becoming saturated to one value. Shutter controller184 checks the values of digital image data and determines whether thereare too many minimum values or too many maximum values. In oneembodiment, if there are too many minimum values, controller 184increases the charge accumulation time of electronic shutter 150, and ifthere are too many maximum values, controller 184 decreases the chargeaccumulation time of electronic shutter 150.

The overall size of photo detector array 148 is preferably large enoughto receive an image having several features. Images of such spatialfeatures produce translated patterns of pixel information as opticalmouse 10 moves over a surface. The number of photo detectors in array148 and the frame rate at which their contents are captured anddigitized cooperate to influence how fast optical mouse 10 can be movedacross a surface and still be tracked. Tracking is accomplished bycorrelator 160 by comparing a newly captured sample frame with apreviously captured reference frame to ascertain the direction andamount of movement.

In one embodiment, the entire content of one of the frames is shifted bycorrelator 160 by a distance of one pixel successively in each of theeight directions allowed by a one pixel offset trial shift (one over,one over and one down, one down, one up, one up and one over, one overin the other direction, etc.). That adds up to eight trials. Also, sincethere might not have been any motion, a ninth trial “null shift” is alsoused. After each trial shift, those portions of the frames that overlapeach other are subtracted by correlator 160 on a pixel by pixel basis,and the resulting differences are preferably squared and then summed toform a measure of similarity (correlation) within that region ofoverlap. In another embodiment, larger trial shifts (e.g., two over andone down) may be used. The trial shift with the least difference(greatest correlation) can be taken as an indication of the motionbetween the two frames. That is, it provides raw movement informationthat may be scaled and or accumulated to provide movement information(ΔX and ΔY) 161 of a convenient granularity and at a suitable rate ofinformation exchange, which is output to a host device.

In one embodiment, sensor 16 is configured to distinguish betweenambient light and light from light source 2, and detect when opticalmouse 10 is lifted away from surface 6 by sensing the level of lightfrom light source 2 that is reflected from surface 6. When optical mouse10 is lifted away from surface 6, the light from light source 2 nolonger reaches photo detector 162 and the photo detectors in array 148in the same quantity that it did previously, if at all; the reflectingsurface 6 is too far away or is simply not in view. However, when mouse10 is lifted, ambient light from other light sources (e.g., fluorescentlights, a cathode ray tube (CRT), sunlight, etc.) may strike the photodetectors, and the outputs of the photo detectors will vary based on theintensity of the ambient light.

In one embodiment, sensor 16 modulates the light from light source 2 ata frequency that is unlikely to occur in ambient light from other lightsources that may be present near the mouse 10, which allows sensor 16 todistinguish between light received from light source 2 and lightreceived from ambient light sources. When the strength of the reflectedmodulated light from light source 2 falls below a predeterminedthreshold value, indicating that mouse 10 has likely been lifted fromsurface 6, sensor 16 reports zero motion to the host device so that thescreen pointer is held steady.

Ambient light that may cause interference with the operation of mouse 10is typically at a low frequency, such as less than 200 Hertz (Hz). CRT'sand fluorescent lights are typically the most problematic. CRT'stypically flash at up to about 100 Hz, and fluorescent lights in theUnited States typically flash at 120 Hz. In one embodiment, light source2 is modulated to provide light flashes or light pulses at asubstantially higher frequency than such ambient light sources.

Light source 2 turns on when it receives a pulse from sensor 16. Theamount of time that light source 2 remains on is determined by the width(duration) of the received pulse. In previous optical mice, when themouse was being moved, 1500 images per second were typically captured,with the light source being flashed once for each captured image (i.e.,a flash rate of 1500 flashes per second), and with a typical flashduration between about ten and one hundred microseconds for each flash.In one embodiment of the present invention, rather than turning on thelight source 2 with a single, relatively wide pulse of the desiredduration (e.g., one hundred microseconds) to capture an image, a highfrequency digital modulation is used to modulate a wide pulse, andthereby generate many pulses having a smaller width that provide thesame effective illumination as a single wide pulse.

In one embodiment, light controller 180 outputs a pulse to multiplier(modulator) 178 during each frame period that an image is to becaptured. In one form of the invention, the pulses output by lightcontroller 180 have a width of twice the desired duration of on time oflight source 2 for a particular image to be captured. In one embodiment,oscillator 176 generates a 100 KHz square wave, which is output tomultiplier 178 and multiplier 166. In other embodiments, frequenciesother than 100 KHz are used for the modulation waveform output byoscillator 176. Multiplier 178 multiplies the pulse received from lightcontroller 180 by the square wave received from oscillator 176, andoutputs the resulting modulated signal to light source 2.

For example, if a one hundred microsecond duration of on time of lightsource 2 is desired for each image to be captured, rather than drivinglight source 2 with a single pulse having a width of one hundredmicroseconds, in one form of the invention, light controller 180 outputsa pulse having a width of two hundred microseconds to multiplier 178.Multiplier 178 multiplies the received pulse by the 100 KHz square wavereceived from oscillator 176, resulting in a modulated signal thatdrives light source 2. The modulated signal includes twenty cycles of a100 KHz square wave, with a total duration of two hundred microsecondsand a cumulative on time of one hundred microseconds. The photo detectorarray 148 integrates the same amount of signal in each frame for themultiple narrower pulses as for a single wider pulse, and deliversidentical images to those that would be delivered using a single widerpulse.

In one embodiment, a synchronous detection technique is used to detectthe modulated light signal output by light source 2 and reflected bysurface 6. In one form of the invention, a photo detector 162 separatefrom the photo detector array 148 is used to synchronously detect themodulated light from light source 2 in a continuous time manner. Theelectrical signal output by photo detector 162 is amplified by amplifier164. In one embodiment, amplifier 164 is AC coupled to photo detector162, and clips for large signals in order to cover a large dynamicrange. Multiplier (demodulator) 166 multiplies the amplified signal fromamplifier 164 by the modulation waveform (e.g., 100 KHz square wave)output by oscillator 176.

In one form of the invention, multiplier 166 alternately multiplies by+1 then −1, so that the AC signals at the 100 KHz modulation frequency(i.e., the signals generated from light received from light source 2)output by amplifier 164 are synchronously rectified (i.e., demodulateddown to a DC or low frequency signal), resulting in a demodulated signalthat is passed through low pass filter 168 to comparator 172. Forsignals output by photo detector 162 that are at frequencies differentthan the modulation frequency (i.e., signals generated from lightreceived from ambient light sources), these signals are typically DC orlow frequency signals (e.g., 60 or 120 Hz) that are converted to highfrequency signals when multiplied by the alternating +1 and −1 100 KHzsquare wave by multiplier 166. The high frequency signals output bymultiplier 166 are blocked by low pass filter 168, so the output of lowpass filter 168 will be near zero for such signals. Thus, photo detector162 is essentially gated at the same frequency that the light source 2is being flashed, so that ambient light is blocked, and the magnitude oflight from light source 2 can be detected.

Comparator 172 includes a first input 170A coupled to the output of lowpass filter 168, and a second input 170B coupled to a threshold voltage.Comparator 172 compares the signal received from low pass filter 168with the threshold value, and thereby determines whether there is asufficient amount of light from light source 2 reaching the photodetectors 148. If the signal received from low pass filter 168 fallsbelow the threshold value, indicating that there is an insufficientamount of light from light source 2 reaching the photo detectors 148,and that mouse 10 has likely been lifted away from surface 6, comparator172 outputs a low signal indication or “mouse lifted” signal 174 tocorrelator 160.

Components of the electrical signal generated by photo detector 162based on ambient light are filtered out, and do affect the signal outputto the comparator 172, even though the ambient light does affect theoutput of the photo detector array 148. In cases where photo detectorarray 148 generates poor (e.g., out of focus) images because ofexcessive ambient light, and very little light from light source 2strikes the photo detector array 148, the separate path, including photodetector 162, amplifier 164, multiplier 166, low pass filter 168, andcomparator 172, detects the problem, and comparator 172 outputs a mouselifted signal 174 to correlator 160.

In one embodiment, when correlator 160 receives a mouse lifted signal174, correlator 160 suppresses normal motion calculations from thecaptured images and stops reporting motion data 161 or reports zeromotion, resulting in a freeze in the screen pointer position at whateverlocation it currently occupies, when it otherwise might jitter randomlyon the screen. When optical mouse 10 is subsequently replaced on surface6, comparator 172 detects that the signal received from low pass filter168 exceeds the threshold value, comparator 172 suppresses the mouselifted signal 174, and correlator 160 resumes generating movement data161 from captured images in the normal manner.

In another embodiment, rather than using a multiplier 166 to demodulatethe modulated light signal from light source 2 down to a low frequency,an AC tuned filter and envelope detection circuitry may be used toconvert the signal back to a DC or low-frequency indication of thestrength of the received signal from light source 2.

For the embodiment shown in FIG. 2, a photo detector 162 separate fromphoto detector array 148 is used to detect the level of reflectedmodulated light from light source 2. In the embodiments illustrated inFIGS. 3A and 4A, the photo detector array 148 itself is used indetecting the magnitude of reflected modulated light from light source2.

FIG. 3A is an electrical schematic/block diagram illustrating lightsensing circuitry 300 of optical mouse 10 with two capacitors per pixelor photo detector in array 148 according to one embodiment of thepresent invention. A single pixel circuit of array 148 is illustrated inFIG. 3A. It will be understood by persons of ordinary skill in the artthat in a complete array 148, portions of the illustrated circuitry 300will be replicated a number of times based on the number of pixels inarray 148.

Light sensing circuitry 300 includes oscillator 176, inverter 304, ANDgates 306 and 308, switch 312, switch 314, capacitor 316, switch 318,switch 320, capacitor 322, switch 324, and photodiode 328. In oneembodiment, oscillator 176 generates a square wave, which is output toinverter 304 and to AND gate 306. AND gate 306 includes inputs 306A and306B, and output 306C. AND gate 306 receives the square wave fromoscillator 176 at input 306A. AND gate 308 includes inputs 308A and308B, and output 308C. Inverter 304 inverts the square wave receivedfrom oscillator 176, and outputs an inverted square wave to input 308Bof AND gate 308. Input 306B of AND gate 306 and input 308A of AND gate308 are coupled to shutter controller 184 (shown in FIG. 2), whichoutputs shutter signal 182.

Switch 314 is controlled by the output 306C of AND gate 306. Switch 320is controlled by the output 308C of AND gate 308. When shutter signal182 is low, the outputs of AND gates 306 and 308 are low, and switches314 and 320 are open. When shutter signal 182 is high, AND gate 306outputs a square wave to switch 314, and AND gate 308 outputs aphase-shifted square wave to switch 320. Because of the signal inversioncaused by inverter 304, the square wave output by AND gate 308 is phaseshifted by 180 degrees with respect to the square wave output by ANDgate 306. When the square wave output by AND gate 306 is high, switch314 is closed, and when this square wave is low, switch 314 is open.Similarly, when the square wave output by AND gate 308 is high, switch320 is closed, and when this square wave is low, switch 320 is open.

Switch 312 is controlled by the shutter signal 182 output by shuttercontroller 184. When shutter signal 182 is high, switch 312 is closed.And when shutter signal 182 is low, switch 312 is open. Light sensingcircuitry 300 is described in further detail below with reference toFIG. 3B.

FIG. 3B is a timing diagram illustrating the timing of control signalsfor the light sensing circuitry 300 shown in FIG. 3A. Shutter signal 182includes a series of pulses that are generated by shutter controller 184(shown in FIG. 2). When shutter signal 182 is high, light source 2 isflashed on and off at a frequency determined by the frequency ofoscillator 176. The signal from light source 2 is represented by lightsource signal 340 in FIG. 3B, with a high value corresponding to thelight source 2 being on, and a low value corresponding to the lightsource 2 being off. The output of AND gate 306 is represented by I_(A)signal 342, which is a square wave with the same phase and frequency aslight source signal 340 when shutter signal 182 is high, and is low whenshutter signal 182 is low. The output of AND gate 308 is represented byI_(B) signal 344, which is a square wave with the same frequency aslight source signal 340 (and I_(A) signal 342) when shutter signal 182is high, and is low when shutter signal 182 is low. As shown in FIG. 3B,I_(B) signal 344 is 180 degrees out of phase with signals 340 and 342.

Although three pulses are shown for signals 340, 342, and 344 whileshutter signal 182 is high, the number of pulses during this period willdepend on the pulse width of the shutter signal 182, and the frequencyof oscillator 176. For example, assuming that a shutter signal 182 witha pulse width of one hundred microseconds is generated for each image tobe captured, and that the light source 2 is modulated with a 100 KHzsquare wave, then ten pulses of light five microseconds wide with fivemicrosecond gaps between each pulse occur during each shutter opening.For this example, signals 340, 342, and 344 would include ten pulseswith a five microsecond duration and a five microsecond low periodbetween each pulse.

In one form of the invention, each pixel circuit in photo detector array148 includes two storage capacitors 316 and 322. In one embodiment, thelight received by each pixel during the light source 2 on timesgenerates charge that is accumulated on the pixel's capacitor 316, whilethe light received by each pixel during the light source 2 off timesgenerates charge that is accumulated on the pixel's capacitor 322. Morespecifically, when shutter signal 182 goes high, switch 312 closes,thereby connecting photo diode 328 between power supply (VDD) 310 andground 302. When shutter signal 182 is high, and I_(A) signal 342 goeshigh, switch 314 closes (switch 320 is open since I_(B) signal 344 islow when I_(A) signal 342 is high), thereby allowing the photo currentfrom photodiode 328 to charge capacitor 316. When shutter signal 182 ishigh, and I_(B) signal 344 goes high, switch 320 closes (switch 314 isopen since I_(A) signal 342 is low when I_(B) signal 344 is high),thereby allowing the photo current from photodiode 328 to chargecapacitor 320.

Switches 318 and 324 are controlled by R_(A) signal 346 and R_(B) signal348, respectively. When R_(A) signal 346 is high, switch 318 is closed.And when R_(A) signal 346 is low, switch 318 is open. When R_(B) signal348 is high, switch 324 is closed. And when R_(B) signal 348 is low,switch 324 is open. At some point after the end of the shutter time(i.e., after shutter signal 182 goes low), R_(A) signal 346 goes high,closing switch 318, and connecting capacitor 316 to amplifier 157. Thevoltage on capacitor 316 is amplified by amplifier 157 and converted toa digital value by analog-to-digital converter 158. At some point afterR_(A) signal 346 goes low, R_(B) signal 348 goes high, closing switch324, and connecting capacitor 322 to amplifier 157. The voltage oncapacitor 322 is amplified by amplifier 157 and converted to a digitalvalue by analog-to-digital converter 158. Analog-to-digital converter158 outputs the digital values to correlator 160 (shown in FIG. 2).

In one embodiment, each of the pixels in array 148 include twocapacitors 316 and 322 and generate two voltages in the same manner asdescribed above with reference to FIGS. 3A and 3B. The light received byarray 148 during the light source 2 on times generates charge that isaccumulated on the first capacitor 316, while the light received byarray 148 during the light source 2 off times generates charge that isaccumulated on the second capacitor 322. Ambient light contributes tothe accumulated charge during both on times and off times of lightsource 2. For each image acquired by array 148, each pixel in the array148 outputs two voltages—a first voltage (from capacitor 322)representing the sensed amount of ambient light, and a second voltagerepresenting the combined amount of sensed ambient light and sensedlight from light source 2. The two voltages output by each pixel areconverted to corresponding first and second digital values byanalog-to-digital converter 158, which are provided to correlator 160.In one embodiment, correlator 160 determines the amount of lightincident on array 148 from light source 2 by subtracting the first valuerepresenting the amount of ambient light from the second valuerepresenting the combined amount of ambient light and light from lightsource 2.

The values obtained by subtracting the first value representing theamount of ambient light from the second value representing the combinedamount of ambient light and light from light source 2 are referred toherein as a filtered digital image, since the ambient light hasessentially been filtered out. In one embodiment, correlator 160correlates these filtered digital images to generate movementinformation 161. If there is a lot of ambient light on the area underthe mouse 10 that is being imaged, this ambient light can interfere withnavigation accuracy during normal use of the mouse 10. By filtering outthe ambient light from the captured images, better navigation accuracyis provided.

In one embodiment, if the level of light from light source 2 calculatedby correlator 160 falls below a given threshold value, indicating thatthere is an insufficient amount of light from light source 2 reachingthe photo detectors 148, and that mouse 10 has likely been lifted awayfrom surface 6, correlator 160 suppresses normal motion calculationsfrom the captured images and stops reporting motion data 161 or reportszero motion, resulting in a freeze in the screen pointer position atwhatever location it currently occupies.

FIG. 4A is an electrical schematic/block diagram illustrating lightsensing circuitry 400 of optical mouse 10 with one capacitor per pixelor photo detector in array 148 according to another embodiment of thepresent invention. A single pixel circuit of array 148 is illustrated inFIG. 4A. It will be understood by persons of ordinary skill in the artthat in the complete array 148, portions of the illustrated circuitry400 will be replicated a number of times based on the number of pixelsin array 148.

Light sensing circuitry 400 includes oscillator 176, inverter 404, ANDgates 406 and 408, inverter 409, switches 412, 414, 415, 420, and 424,transistors 417 and 419, capacitor 422, and photo detector 428. In oneembodiment, transistors 417 and 419 are P-type Metal Oxide Semiconductor(PMOS) Field Effect Transistors (FET's). In one embodiment, oscillator176 generates a square wave, which is output to inverter 404 and to ANDgate 406. AND gate 406 includes inputs 406A and 406B, and output 406C.AND gate 406 receives the square wave from oscillator 176 at input 406A.AND gate 408 includes inputs 408A and 408B, and output 408C. Inverter404 inverts the square wave received from oscillator 176, and outputs aninverted square wave to input 408B of AND gate 408. Input 406B of ANDgate 406 and input 408A of AND gate 408 are coupled to shuttercontroller 184 (shown in FIG. 2), which outputs shutter signal 182.

Switch 414 is controlled by the output 408C of AND gate 408. Switch 415is controlled by the output 408C of AND gate 408 after being inverted byinverter 409. Switch 420 is controlled by the output 406C of AND gate406. When shutter signal 182 is low, the outputs of AND gates 406 and408 are low, switches 414 and 420 are open, and switch 415 is closed.When shutter signal 182 is high, AND gate 406 outputs a square wave toswitch 420, and AND gate 408 outputs a phase-shifted square wave toswitch 414. Because of the signal inversion caused by inverter 404, thesquare wave output by AND gate 408 is phase shifted by 180 degrees withrespect to the square wave output by AND gate 406. When the square waveoutput by AND gate 406 is high, switch 420 is closed, and when thissquare wave is low, switch 420 is open. When the square wave output byAND gate 408 is high, switch 414 is closed, and when this square wave islow, switch 414 is open. Inverter 409 inverts the square wave output byAND gate 408, so when the square wave output by AND gate 408 is high,switch 415 is open, and when this square wave is low, switch 415 isclosed.

Switch 412 is controlled by the shutter signal 182 output by shuttercontroller 184. When shutter signal 182 is high, switch 412 is closed.And when shutter signal 182 is low, switch 412 is open. Light sensingcircuitry 400 is described in further detail below with reference toFIG. 4B.

FIG. 4B is a timing diagram illustrating the timing of control signalsfor the light sensing circuitry 400 shown in FIG. 4A. Shutter signal 182includes a series of pulses that are generated by shutter controller 184(shown in FIG. 2). When shutter signal 182 is high, light source 2 isflashed on and off at a frequency determined by the frequency ofoscillator 176. The signal from light source 2 is represented by lightsource signal 440 in FIG. 4B, with a high value corresponding to thelight source 2 being on, and a low value corresponding to the lightsource 2 being off. The output of AND gate 406 is represented by I_(UP)signal 442, which is a square wave with the same phase and frequency aslight source signal 440 when shutter signal 182 is high, and is low whenshutter signal 182 is low. The output of AND gate 408 is represented byI_(DN) signal 444, which is a square wave with the same frequency aslight source signal 440 (and I^(UP) signal 442) when shutter signal 182is high, and is low when shutter signal 182 is low. As shown in FIG. 4B,I_(DN) signal 444 is 180 degrees out of phase with signals 440 and 442.

Although three pulses are shown for signals 440, 442, and 444 whileshutter signal 182 is high, the number of pulses during this period willdepend on the pulse width of the shutter signal 182, and the frequencyof oscillator 176.

In one form of the invention, each pixel circuit in photo detector array148 includes one storage capacitor 422. In one embodiment, the lightreceived by each pixel during the light source 2 off times generatescharge that is accumulated on capacitor 422, while the light received byeach pixel during the light source 2 on times causes capacitor 422 todischarge. More specifically, when shutter signal 182 goes high, switch412 closes, thereby connecting photo diode 428 between power supply(VDD) 410 and ground 402. When shutter signal 182 is high, and I_(UP)signal 442 goes high, switch 420 closes (switch 414 is open since I_(DN)signal 444 is low when I_(UP) signal 442 is high, so transistors 417 and419 are essentially removed from the circuit), thereby allowing thephoto current from photodiode 428 to discharge capacitor 422. Thus, asshown by V_(C) signal 446 in FIG. 4B, which represents the voltage oncapacitor 422 over time, the voltage ramps down during the time that thelight source 2 is on, with a slope that depends on the combined amountof ambient light and light from light source 2 incident on the array148.

When shutter signal 182 is high, and I_(DN) signal 444 goes high, switch414 closes and switch 415 opens (switch 420 is open since I_(UP) signal442 is low when I_(DN) signal 444 is high), thereby allowing the photocurrent from photo diode 428 to charge capacitor 422. Transistors 417and 419 are in a current mirror configuration. The photo current fromphotodiode 428 is replicated by the current mirror, and flows downthrough transistor 419 to charge capacitor 422. Thus, as shown by V_(C)signal 446, the voltage on capacitor 422 ramps up during the time thatthe light source 2 is off, and only ambient light is incident on thearray 148. The slope of the ramp up depends on the amount of ambientlight incident on the array 148. The difference between the startingvoltage of capacitor 422 (when shutter signal 182 goes high) and theending voltage of capacitor 422 (when shutter signal 182 goes low) is avoltage 447 that represents the amount of light from light source 2.

Switch 424 is controlled by Read signal 448. When Read signal 448 ishigh, switch 424 is closed. And when Read signal 448 is low, switch 424is open. At some point after the end of the shutter time (i.e., aftershutter signal 182 goes low), Read signal 448 goes high, closing switch424, and connecting capacitor 422 to amplifier 157. The voltage oncapacitor 422 is amplified by amplifier 157 and converted to a digitalvalue by analog-to-digital converter 158. Analog-to-digital converter158 outputs the digital values to correlator 160 (shown in FIG. 2).

In one embodiment, each of the pixels in array 148 includes onecapacitor 422, and generates voltages in the same manner as describedabove with reference to FIGS. 4A and 4B. For each image acquired byarray 148, each pixel in the array 148 outputs a voltage that, withreference to an initial voltage, represents the sensed amount of lightfrom light source 2. The voltages output by each pixel are converted todigital values by analog-to-digital converter 158, which are provided tocorrelator 160. These digital values are referred to herein as afiltered digital image, since the ambient light has essentially beenfiltered out. In one embodiment, correlator 160 correlates thesefiltered digital images to generate movement information 161. Byfiltering out the ambient light from the captured images, betternavigation accuracy is provided.

In one embodiment, if the level of light from light source 2 determinedby correlator 160 falls below a given threshold value, indicating thatthere is an insufficient amount of light from light source 2 reachingthe photo detectors 148, and that mouse 10 has likely been lifted awayfrom surface 6, correlator 160 suppresses normal motion calculationsfrom the captured images and stops reporting motion data 161 or reportszero motion, resulting in a freeze in the screen pointer position atwhatever location it currently occupies.

The time that shutter signal 182 is high is referred to as a shutterinterval. As shown in FIGS. 3B and 4B, the shutter interval hasessentially been divided into three subintervals, with three lightpulses during each shutter interval. Since ambient light (and light fromlight source 2) are not necessarily constant, there is a tradeoff interms of how many subintervals to break up the shutter interval into.More (smaller) subintervals allow better interleaving (and balance)between the light source 2 on and light source 2 off phases. It alsoallows a bigger dynamic range for the embodiment shown in FIG. 4A sinceshorter subintervals of potentially large ambient signal are integrated.Less subintervals are simpler to implement and reduce charge injectionnoise.

In one embodiment, optical motion sensor 16 is configured to beimplemented in an optical mouse for a desktop personal computer,workstation, portable computer, or other device. In another embodiment,optical motion sensor 16 may also be implemented in an opticaltrackball, an optical fingerprint sensing pointing device, or otherpointing device.

It will be understood by a person of ordinary skill in the art thatfunctions performed by optical motion sensor 16 may be implemented inhardware, software, firmware, or any combination thereof. Theimplementation may be via a microprocessor, programmable logic device,or state machine. Components of the present invention may reside insoftware on one or more computer-readable mediums. The termcomputer-readable medium as used herein is defined to include any kindof memory, volatile or non-volatile, such as floppy disks, hard disks,CD-ROMs, flash memory, read-only memory (ROM), and random access memory.

One form of the present invention provides an optical mouse with a liftdetection mechanism that is more reliable than prior techniques, andthat correspondingly provides lower power consumption than prior opticalmice. One form of the present invention provides an optical mouse thatmodulates the light from the mouse light source to facilitate detectingwhen the mouse is up in the air and the screen pointer should not bemoving. Another form of the present invention provides an optical mousethat modulates the light from the mouse light source so that if there isambient light mixed in with the light from the mouse light source, themouse is able to reject the ambient light and prevent the ambient lightfrom interfering with the normal operation of the mouse. Yet anotherembodiment of the invention provides an optical mouse that modulates thelight from the mouse light source to detect when the mouse is lifted, aswell as to be able to reject the ambient light during normal operation.In one form of the invention, a separate photo detector is used todetect when the mouse has been lifted. In another form of the invention,rather than using a separate photo detector, the photo detector arrayused for capturing images for generating movement information is alsoused in detecting the mouse lifted condition, as well as in rejectingambient light.

Although specific embodiments have been illustrated and described hereinfor purposes of description of the preferred embodiment, it will beappreciated by those of ordinary skill in the art that a wide variety ofalternate and/or equivalent implementations may be substituted for thespecific embodiments shown and described without departing from thescope of the present invention. Those with skill in the mechanical,electro-mechanical, electrical, and computer arts will readilyappreciate that the present invention may be implemented in a very widevariety of embodiments. This application is intended to cover anyadaptations or variations of the preferred embodiments discussed herein.Therefore, it is manifestly intended that this invention be limited onlyby the claims and the equivalents thereof.

1. A method for detecting when an optical mouse has been lifted from an imaging surface, the method comprising: illuminating the imaging surface with a modulated light signal output by the mouse, thereby generating a reflected modulated light signal; generating an electrical signal based on sensed light, the sensed light including ambient light and the reflected modulated light signal; processing the electrical signal to remove components corresponding to the ambient light, including upconverting a frequency of components corresponding to the ambient light based on a modulation waveform that is used to generate the modulated light signal; and determining whether the mouse has been lifted from the imaging surface based on the processed electrical signal.
 2. The method of claim 1, and further comprising: detecting the magnitude of the sensed reflected modulated light signal based on the processed electrical signal; and generating a mouse lifted indication if the magnitude of the sensed reflected modulated light signal falls below a threshold value.
 3. The method of claim 1, and further comprising: generating the modulation waveform, wherein the modulation waveform is a square wave having a frequency of greater than about 10 KHz; generating a modulated light control signal based on the modulation waveform; and outputting the modulated light control signal to a light source of the mouse to generate the modulated light signal.
 4. The method of claim 3, and further comprising: demodulating the electrical signal based on the modulation waveform.
 5. A method for generating movement data with an optical pointing device for controlling the position of a screen pointer, the method comprising: illuminating an imaging surface with a light source, thereby generating reflected light; sensing a combination of reflected light from the light source and ambient light when the light source is on; sensing ambient light when the light source is off; generating digital images based on a difference between the sensed combination and the sensed ambient light; generating movement data based on the digital images, the movement data indicative of relative motion between the imaging surface and the pointing device; charging a capacitor when the light source is off during a shutter interval; discharging the capacitor when the light source is on during the shutter interval; and wherein the difference between the voltage on the capacitor at the beginning of the shutter interval and the voltage on the capacitor at the end of the shutter interval represents an amount of sensed reflected light from the light source.
 6. The method of claim 5, and further comprising: generating movement data indicating zero motion if the amount of sensed reflected light from the light source is less than a threshold value.
 7. A method for rejecting ambient light in an optical mouse, the method comprising: illuminating an object with a modulated light signal from the optical mouse, thereby generating a reflected modulated light signal; generating an electrical signal with the optical mouse based on sensed light, the sensed light including ambient light and the reflected modulated light signal; and processing the electrical signal with the optical mouse to remove components corresponding to the ambient light, including upconverting a frequency of components corresponding to the ambient light based on a modulation waveform that is used to generate the modulated light signal.
 8. The method of claim 7, and further comprising: detecting the magnitude of the sensed reflected modulated light signal based on the processed electrical signal.
 9. The method of claim 7, and further comprising: generating the modulation waveform; generating a modulated light control signal based on the modulation waveform; and outputting the modulated light control signal to a light source of the digital imaging system to generate the modulated light signal.
 10. The method of claim 9, and further comprising: demodulating the electrical signal based on the modulation waveform. 